The company which has taken over the East Midlands rail franchise has admitted to facing challenges after some claimed standards had fallen.
East Midlands Trains said it had inherited problems
East Midlands Trains took over from Midland Mainline and Central Trains on 11 November promising better services.
But some customers have said older trains with fewer carriages are being used on the old Central Trains routes.
East Midlands Trains said parts of the current service were "unacceptable" but improvements were on the way.
The company attracted criticism even before it took over the franchise because of plans to scrap free tea and coffee and buffet cars.
But Paul Clark, a member of passenger group Travel Watch, highlighted early concerns over day to day services.
"It does look as though the newer trains have been diverted elsewhere," he said.
"Conditions are slightly worse, but to be fair it is early days and what really matters is that if in two or three months there are still fewer carriages then that is a real cause for concern."
David Horne, commercial director for East Midlands Trains, admitted some older trains had been used and some services had fewer carriages - but that the number was very small.
"We have taken over the fleet that Central Trains used and have brought in some more from the south.
"But we are not happy about the condition these trains are in - they are too dirty and they are not reliable enough.
"Unfortunately this was all that was available and we do have a programme of works to improve them."
He added: "The current situation is absolutely unacceptable but it is a position we have inherited and it is a short term situation while we reorganise the service."